1. Field of the Invention
This invention relates generally to re-polarization means for generating circularly polarized electromagnetic waves.
2. Description of the Prior Art
Primary radiators, as for example, for search and target tracking radar antennas usually have linear polarization. However, the use of circular polarization is desirable in radar applications so as to reduce reflection effects of rain clouds and thus the linear polarization of the antenna is frequently converted by a lattice structure placed in front of the antenna aperture so as to obtain circular polarization. Such polarization converters using lattice structures are known as, for example, as shown in U.S. Pat. No. 3,754,271. This patent discloses meander lines which extend at 45.degree. to the E-vector which is the electrical field vector of the instant wave and they generate a phase difference due to the capacitive or inductive influence of the E-vector components which lie perpendicular and parallel to the meander lines and a phase difference of 90.degree. is necessary for this circular polarization and this is achieved with suitable dimensioning and layering.
Other types of lattice structures consist of straight lines at specific intervals in a plurality of layers as well as line and rectangular combinations for generating circular polarization. The suppression or decoupling of the cross-polarization or in general of the orthogonal or de-polarization with respect to a desired linear or circular polarization is of great importance in many applications. For example, so as to avoid cross-talk utilizing double polarization operation or in order to achieve the necessary precision in position finding methods. For this purpose, lattices with metal strips or wires extend perpendicular with respect to the E-vector can be employed in a known manner with linear polarization. The cross-polarization component which extends parallel to the wires is reflected and is thus suppressed. By using a plurality of such lattice layers, the degree of suppression of the cross-polarization components can be further accomplished.